Prjpluto is a fork of buildroot designed to create complete embedded distributions for Cortex-M processors.
THIS IS STILL CONSIDERED PRETTY ALPHA 
The goal is to generate everything needed to develop and program and debug on embedded ARM Cortex-M series processors.
It generates:
The toolchain
The RTOS (in this case a modified Nuttx)
The software for icsp programming and debugging (openocd and gdb) 

Eventually I hope to support other RTOSes for Cortex-M series processors. 

Nuttx is a mostly posix compliant RTOS. It handles multiple processes and peripheral device drivers. It is very similar to linux. It also has a command line shell. 
I have modified it a bit to act more like a true kernel. It also integrates in the buildroot generated filesystem into the Nuttx binary so that the files are available at run time. 

Instructions are at http://www.vxmdesign.com/STM32.html

Right now it has been tested against the STM32F407 discovery board with baseboard using the vdsc_defconfig

(This is the original buildroot readme) 

To build and use the buildroot stuff, do the following:

1) run 'make menuconfig'
2) select the packages you wish to compile
3) run 'make'
4) wait while it compiles
5) Use your shiny new root filesystem. Depending on which sort of
    root filesystem you selected, you may want to loop mount it,
    chroot into it, nfs mount it on your target device, burn it
    to flash, or whatever is appropriate for your target system.

You do not need to be root to build or run buildroot.  Have fun!

Offline build:
==============

In order to do an offline-build (not connected to the net), fetch all
selected source by issuing a
$ make source

before you disconnect.
If your build-host is never connected, then you have to copy buildroot
and your toplevel .config to a machine that has an internet-connection
and issue "make source" there, then copy the content of your dl/ dir to
the build-host.

Building out-of-tree:
=====================

Buildroot supports building out of tree with a syntax similar
to the Linux kernel. To use it, add O=<directory> to the
make command line, E.G.:

$ make O=/tmp/build

And all the output files (including .config) will be located under /tmp/build.

More finegrained configuration:
===============================

You can specify a config-file for uClibc:
$ make UCLIBC_CONFIG_FILE=/my/uClibc.config

And you can specify a config-file for busybox:
$ make BUSYBOX_CONFIG_FILE=/my/busybox.config

To use a non-standard host-compiler (if you do not have 'gcc'),
make sure that the compiler is in your PATH and that the library paths are
setup properly, if your compiler is built dynamically:
$ make HOSTCC=gcc-4.3.orig HOSTCXX=gcc-4.3-mine

Depending on your configuration, there are some targets you can use to
use menuconfig of certain packages. This includes:
$ make HOSTCC=gcc-4.3 linux-menuconfig
$ make HOSTCC=gcc-4.3 uclibc-menuconfig
$ make HOSTCC=gcc-4.3 busybox-menuconfig

Please feed suggestions, bug reports, insults, and bribes back to the
buildroot mailing list: buildroot@buildroot.org